I personally use this battery
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/202628761231
On a 1806 motor with a 6030 prop on the Tiny Trainer I was getting about 10-14 minutes a battery depending on how much gliding I did. $8 a piece and free shipping from the states. $15 for 2. They work pretty good. I've had em for about 3 years now with maybe 50+ flights and they still work fine. They work good on any of the minis as well. Not much heavier than the 500mah but WAY more flight time.
A warning tho, they are cheaper batteries. As with most electronics, you get what you pay for. One battery shipped to me wouldn't charge on my charger using lipo settings, the voltage was too low. I had to charge it on a NiMH setting for 20 seconds to bump up the voltage enough to then charge with the lipo setting. Basically the manufacturer didn't properly give the battery a storage charge. The battery works fine now, but just something to keep an eye out for when purchasing cheaper batteries.
And I agree with the above, I wouldn't use anything over 850mah on the Tiny Trainer or any mini.